Change circle segment depends on diameter
Your operator does nothing. It's missing an execute or invoke function.

To do what you want to do, you could create a modal operator:


In its invoke function you would create a circle curve object.
In it's modal function you would change the U resolution of the curve and the scale, for instance based on mouse movement
when confirming the modal, you would convert the curve to a mesh (if that is what you want)


Check the template scripts in Blender to understand how operators are structured.